The chlorination of carboxylic group of .alpha.-aminoacids by means of the usual chlorinating agents such as PCl.sub.5, PCl.sub.3, Cl.sub.2, SOCl.sub.2, etc. often presents synthesis difficulties due both to the steric hindrance and to the presence of various substituents. Among the hardly chlorinatable aminoacids there is for instance included p-hydroxyphenylglycine, since, among other things, the presence of hydroxyl group on the benzene ring considerably disturbs the production of acyl chloride and besides the obtention of the product in crystalline and stable form is difficult, which form is necessary for an effective recovering from the reaction mixture.
Among the many attempts aiming at attaining the chlorination on the carboxylic group of p-OH-phenylglycine, two processes had a certain success, the first of them, which is based on the use of phosgene as the chlorinating agent and described in U.S. Pat. No. 3,925,418 as well as by Brenner and Photaki in Helv. Chimica Acta, 1956, pages 1525-26, is rather complex as it consists in forming a cyclic anhydride and successively cleaving with gaseous hydrogen chloride, and further requires the use of phosgene, which gives rise to noticeable plant problems due to its dangerous nature and corrosivity. The second process is based on the use of chloromethylene-dimethylammonium chloride as the chlorinating agent and is described in the U.S. patent application Ser. No. 29,126 filed Apr. 11, 1979 now U.S. Pat. No. 4,272,454 in the name of same applicants.